The exemplary embodiment relates to printing systems. It relates particularly to a magnetic brush roll and method for suppressing unwanted toner emissions from a developer unit and will be described with reference thereto.
In typical electrophotographic image forming devices, such as copy machines and laser beam printers, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developer material. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to the print medium, such as a sheet of paper. The fusing of the toner image onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is permanently affixed to the copy paper in the fusing process.
The toner is stored in a developer unit and delivered from the unit onto the photoreceptor by a magnetic brush system. The brush rotates and is replenished with toner and carrier granules as it reenters the developer unit. There is a tendency for toner particles to be emitted from the magnetic brush system or from the developer housing into the surrounding atmosphere. Toner emissions from a xerographic magnetic brush system can contaminate the developer and reduce the reliability of other components of the image forming device.
The toner emissions may coat surfaces which are sensitive to such contamination, causing them to malfunction. One such surface is the scorotron grid, where, for example, if too much toner contamination alights, an overvoltage condition on the charged photoreceptor occurs. This, in turn, can give rise to image quality problems or induce a sudden and uncontrolled loss of developer material into the marking engine cavity, which may necessitate a service call. Even if the level of contamination does not cause a reliability issue, for example if it alights on a handle or door visible to the customer, it can present an impression of a poorly operating machine.
Unwanted or uncontrolled toner emissions from within the developer housing can often be inhibited by implementation of various sealing solutions. Emissions from the brush itself have proved more difficult to control. In particular, toner may escape at the edges of the magnetic brush into the atmosphere.